1. Field of Invention
The present invention relates to a propeller shaft for a vehicle, and more particularly, to a propeller shaft for a vehicle, capable of absorbing sufficiently length variation of the shaft to an axial direction with a low collapse load when a vehicle collision occurs and thus absorbing sufficiently collision energy, thereby reducing an injury degree of a passenger at a minimum level.
2. Description of Related Art
Generally, a propeller shaft 10 provided in a rear-wheel drive vehicle refers to a power transmission device for transferring smoothly a driving force of a power train constituting of an engine 1 and a transmission 2 to a rear axle 3, as shown in FIG. 1, wherein enough twist strength has to be ensured so as to transfer smoothly toque and also enough bending rigidity has to be ensured since the propeller shaft is long in an axial direction.
Further, except for the basic characteristics as described in the forgoing, recently safe regulations with respect to collision of a vehicle appears to be a important performance factor, that is, a technology of the propeller shaft has been developed for absorbing sufficiently length variations in an axial direction when a vehicle collision occurs and reducing injury degree of a passenger.
However, the length variation of a conventional propeller shaft 10 in an axial direction is not sufficient due to high collapse load when a vehicle collision occurs, and as a result the impact caused by the collision is not sufficiently absorbed, thereby increasing the injury degree of a passenger.
That is, the conventional propeller shaft 10, as shown in FIG. 2A and FIG. 2B, includes a front coupling 11 to be connected to a transmission 2, a front yoke 12 connected to the front coupling 11, a front tube 13 connected to the front yoke 12, a rear tube 15 connected through a universal joint 14, a rear yoke 16 connected to the rear tube 15, and a rear coupling 17 to be connected to a rear axle 3.
Here, the front tube 13 is provided with a diameter variation portion 13a processed through a swaging process wherein it is classified into a small diameter portion 13b extended toward the front yoke 12 and a large diameter portion 13c extended toward the universal joint 14 based on the diameter variation portion 13a. 
The small diameter portion 13b has a smaller diameter than the large diameter portion 13c, and the small diameter portion 13b and the large diameter portion 13c are connected through the diameter variation portion 13a. 
Accordingly, when the impact energy produced during a vehicle collision is transferred to the propeller shaft 10 through the power train, as shown in FIG. 3, the small diameter portion 13b is deformed to be inserted into the large diameter portion 13c while the diameter variation portion 13a is deformed, and thus the propeller shaft 10 absorbs the impact energy through the movement of the small diameter portion 13b as described in the foregoing.
However, since the diameter difference between the small diameter portion 13b and the large diameter portion 13c is not great in the conventional propeller shaft 10, the rear movement amount of the small diameter portion 13b is small and thus the length variation of the propeller shaft in an axial direction is not sufficient due to a high collapse load and the impact energy is not absorbed sufficiently, thereby increasing specially the injury degree of a passenger due to a great deceleration of a vehicle.
Accordingly, in order to make the diameter difference between the small diameter portion 13b and the large diameter portion 13c to be great, an idea that the diameter of the small diameter portion 13b is decreased or the diameter of the large diameter portion 13c is increased may be proposed, but in this case the basic strength of the propeller shaft may vary when the diameter is varied or other drawbacks in accordance with a weight or a package to the surrounding components may be produced.
Further, in order to increase the rear movement amount of the small diameter portion 13b, an idea that the collapse load is decreased by varying property of material may be proposed, but this idea becomes a cause for decreasing the basic strength of the propeller shaft 10.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.